1. Field of the Invention
The present invention relates generally to a construction of a cylinder assembly of an internal combustion engine, particularly of a multi-cylinder internal combustion engine having therein a plurality of engine cylinders in side-by-side relationship. More specifically, the present invention relates to a structure of a coolant circulation system in the cylinder assembly for cooling the same while the engine is driven.
2. Description of the Prior Art
As is well known to those skilled in the art, a cylinder assembly for an internal combustion engine, particularly such a type that has a plurality of engine cylinders therein (hereinafter referred as multi-cylinder engine), is provided with a coolant circulating system for circulating a coolant such as cooling water for the purpose of cooling the engine temperature while the engine is driven. In a multi-cylinder engine, the coolant circulating system comprises a coolant chamber formed within the cylinder block and a coolant return passage connecting the former to a radiator provided exterior of the cylinder assembly. Generally, the cylinder block of the multi-cylinder engine is provided with a plurality of partitions which are substantially parallel to each other. The partitions of each pair are separated from one another to define therebetween an engine cylinder together with an cylinder wall of the cylinder block. The cylinders are arranged within the cylinder block in-line. The coolant chamber is formed within the outer wall and extends therealong so as to surround a substantial part of each combustion chamber. The coolant chamber communicates with a return passage formed within the cylinder head. The cylinder head is tightly secured on the cylinder block to form closed cylinder assembly with clamping a sealing gasket between the head and block. Between the coolant chamber and the return passage, there are provided with a plurality of passages extending laterally with respect to the lined coolant chambers. The lateral passage are formed within the partitions to cool the partitions while the engine is driven.
Indeed, various constructions of the coolant circulating systems for use with a multi-cylinder engine have been developed. One typical construction is disclosed in Japanese Utility Model Publication No. 52-52113 in which a cylinder block is provided with a plurality of coolant chambers separated from each other. Generally the coolant chambers are aligned along an outer wall of the cylinder block. Each of the coolant chambers communicates with a coolant return passage formed within a cylinder head through a sloped passage formed within a partition. One end of the sloped passage opens at the upper surface of the cylinder block to which the cylinder head is fixedly secured. In order to establish communication between the coolant chamber and the return passage, it is a passage is formed within the cylinder head in alignment with the sloped passage. Further, in this constuction, an a opening aligned to with the sloped passage is formed in the sealing member which is interposed between the cylinder block and the cylinder head. In this construction, since the end of the sloped passage is opened at the portion above the engine cylinder, it is quite difficult and troublesome to form the passage in alignment to the sloped passage in the cylinder head. Forming this passage results in increasing the number of processing steps in manufacturing. Further, the passage through the sealing member for communication between the sloped passage and the return passages increases the possibility of leakage of the coolant and/or air/fuel mixture.
Another conventional construction of the coolant circulating system is disclosed in Japanese Utility Model Publication No. 52-54682, published on Dec. 10, 1977. In this publication, a cylinder block is provided with a plurality of separated coolant chambers disposed between adjacent engine cylinders. The coolant chambers are aligned on both sides of the engine cylinders along the side walls of the cylinder block. The coolant chambers are also aligned in the lateral direction with respect to alignment of the combustion chambers and oppose one another on opposite sides of adjacent chambers. Between opposed coolant chambers, a plurality of sloped passages are formed through a partition defining the engine cylinder and the outer wall of the cylinder block. Although this construction of the coolant circulating system can effectively cool the partition, it is difficult to form these sloped passages within the partition, since it is practically impossible to form vertically aligned passages in the partition. Further, during formation of each passage in the substantially X-shaped configuration as shown in FIG. 3 of the publication having two openings on each engine cylinder, a tool for forming the passage, such as drill and the like, is apt to be deformed or damaged at the closed portion of the X-shaped passage. For avoiding these difficulties it is required that the cylinder block be separated into two portions to form the passages. After forming the passages in the partition, the portions are assembled together to form the cylinder block. In this case, some additional and troublesome processing steps are necessary resulting in inefficiency of manufacturing and increasing the of cost therefor.
In each of above-mentioned conventional system, since the sloped passage has an end opening at acute angle with respect to the axis of the engine cylinder, it is difficult to center the for forming tool. For forming the sloped passage at an exact given angle, high processing accuracy is required. This will necessarily cause inefficiency of manufacturing of the cylinder assembly, and thereby cause increased manufacturing cost.
As mentioned above, conventional constructions of coolant circulating systems for engine cylinder assemblies have some quite serious manufacturing problems associated therewith. Furthermore, smaller and lighter cylinder assemblies are required for saving space in a vehicle and for economizing fuel for driving the engine. To achieve this, it has been necessary to reduce the thickness of the partition as much as possible. However, it is difficult to satisfactorily and sufficiently make the partition thinner, since this will possibly cause inefficient of cooling of the partition due to short coolant passages and thereby causes engine overheating. Also, since the coolant circulates and rises through the coolant chamber, coolant passage, return passage and radiator in that order, if the passages formed within the partition are excessively sloped, the coolant may not circulate therethrough.
To avoid the above-mentioned difficulties and disadvantages, there is provided an improved construction of the cylinder assembly in U.S. Pat. No. 3,942,487, issued in Mar. 9, 1976 to Anton Zink. The Zink Patent discloses a cylinder construction comprising a cylinder block having engine cylinders of disposed in-line, and passage means for coolant arranged between the cast cylinder assembly in the area adjacent the surface separating the cylinder block from the cylinder head. The passage means includes a narrow sloped passage which has a depth corresponding at least approximately to that of a piston ring arrangement of the piston at top dead-center position. The narrow sloped passage intersects adjacent coolant chambers and completely separates the cylinder assembly in the lateral direction of the cylinder wall. The passage extends laterally into the cylinder head bolt bore at the interface between the cylinder block and the cylinder head. However, in this construction, increasing the velocity of circulation of the coolant is impossible, because the passage merely connects the coolant chambers adjacent one another. Therefore, it cannot effectively cool the cylinder block, particularly the partitions extending laterally with respect to the cylinder wall to define the engine cylinder. Further, in the Zink Patent, the openings of the sloped passage formed on the top of the cylinder block are so wide as to be impossible to seal completely. Therefore, this may possibly cause leakage of coolant and/or air/fuel mixture.
The present invention solves the abovementioned difficulties for constructing and disadvantages of the use of the prior art arrangement, and therefore provides an improved construction for the coolant circulating system in a cylinder assembly which system can effectively circulate coolant so as to effectively cool the cylinder assembly and yet can be easily constructed.